1. Field of the Invention
The present invention generally relates to a method for fabrication devices on semiconductor substrates. More specifically, the invention relates to a method for removing metallic residue after plasma etching of a metal layer.
2. Description of the Related Art
Magneto-resistive random access memory (MRAM) has been developed as a new type of non-volatile memory. Digital information in MRAM is represented by a direction of magnetization of a magnetic material. MRAM has a plurality of memory cells that are interconnected to one another to facilitate storage of information within the MRAM. A memory cell in a MRAM device generally is a multi-layered structure comprising a pair of magnetic layers separated by a tunnel layer. These layers are deposited as overlying blanket films, layer-by-layer, and then featured to form the MRAM device. More specifically, the MRAM device comprises a free (or top) magnetic layer that may change a direction of magnetization and a bottom magnetic layer that has a fixed direction of magnetization. The magnetic layers are separated by a thin tunnel layer formed of a non-magnetic dielectric material such as aluminum oxide (Al2O3) and the like. The top and bottom magnetic layers may each comprise a plurality of layers of magnetic materials such as permalloy (NiFe), cobalt iron (CoFe), and the like. The top and bottom magnetic layers are also supplied with film electrodes (e.g., comprising conductors such as tantalum (Ta), tantalum nitride (TaN), copper (Cu), and the like) to form an electrical connection for the memory cell to the lines of the MRAM.
Fabrication of a MRAM device comprises etch processes in which one or more layers of a MRAM film stack are removed, either partially or in total. During the etch processes, the metal layers within the MRAM film stack are generally etched using a plasma comprising fluorine or chlorine chemistry. Residues containing metal chlorides and fluorides may build up along the sides of the MRAM film stack and form a conductive veil after the mask is removed. Further, when carbon-based photoresist etch mask is used during the etch processes, a metal-containing polymer may also form upon the MRAM film stack. The conductive residues may cause electrical short-circuits within a MRAM device, e.g., between the magnetic layers separated by the tunnel layer, or may render the MRAM device to operate sub-optimally or not at all.
Therefore, there is a need in the art for a method of removing metallic residue after etching a MRAM film stack.